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ABSTRACT: Pull-down assay and co-immunoprecipitation of cell extracts in which the integrase or reverse transcriptase of Moloney murine leukemia virus was transiently expressed showed that both enzymes interacted with PML proteins. In infected cells, interaction between the integrase and PML was also observed. Transient expression of PIASy and SUMO proteins facilitated SUMOylation of the integrase but had no apparent effects on the interaction with PML. A FLAG-tagged integrase co-localized with PML protein possibly in the PML body. Knockdown of PML by small interfering RNA resulted in reduced viral cDNA levels and integration efficiency. This suggested that PML proteins activated reverse transcription.
Journal of biochemistry 06/2012; 152(2):161-9. · 1.95 Impact Factor
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ABSTRACT: α-Fetoprotein (AFP) is a fetal serum protein abundant in fetal liver whose expression is downregulated in adult liver. The
promoter–proximal region of the AFP gene contains two binding sites for CCAAT/enhancer-binding protein α (C/EBPα), two for
hepatocyte nuclear factor-1α (HNF-1α) and one for nuclear factor-1 (NF-1). Luciferase reporter assays showed that a combination
of C/EBPα, HNF-1α, NF-1 and coactivator p300 gave the maximal activity but the BRG1 and BRM, ATPase subunit of the chromatin
remodeling complex SWI/SNF, repressed the transactivation of the AFP gene by these transcription factors. Deletion analyses
of C/EBPα binding sites suggested that C/EBPα recruited SWI/SNF complex and caused the repression. This repression may also
play important roles in the downregulation of the AFP gene in adult hepatocytes.
Cytotechnology 04/2012; 49(2):143-151. · 1.21 Impact Factor
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ABSTRACT: We previously reported that BRG1, an ATPase subunit of SWI/SNF chromatin remodelling complexes, is constitutively expressed and that the alternative ATPase subunit (BRM) is inducibly expressed through differentiation in mammalian cells. In the present study, the regulatory elements that confer constitutive expression on brg1 were explored. First, we analysed the promoter proximal region surrounding its transcriptional start site. Using computer-aided analysis, a TATA-less, GC-rich promoter containing four putative binding sites for Sp1/3 was predicted. One of the putative Sp1/3-binding sites (from -21 to -15 bp) overlapped with a putative YY1-binding site. A gel-shift assay showed that YY1 but not Sp1/3 bound to this sequence and that Sp3 but not Sp1 bound to the other three predicted binding sites. Furthermore, chromatin immunoprecipitation analysis showed that Sp3 and YY1 bound to the promoter region together with TATA-binding protein in vivo. In vivo and in vitro binding assays showed that Sp3 and YY1 interacted with each other. Together, these results suggest that Sp3 and YY1 recruit general transcription factors and facilitate the assembly of a preinitiation complex.
Journal of biochemistry 03/2011; 149(3):301-9. · 1.95 Impact Factor
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ABSTRACT: The gene for tryptophan oxygenase (TO) is expressed in adult hepatocytes in a tissue- and differentiation-specific manner. The TO promoter has two glucocorticoid-responsive elements (GREs), and its expression is regulated by glucocorticoid hormone in the liver. We found a novel GRE in close proximity to a scaffold/matrix attachment region (S/MAR) that was located around -8.5kb from the transcriptional start site of the TO gene by electrophoretic mobility shift and chromatin immunoprecipitation (ChIP) assays. A combination of nuclear fractionation and quantitative PCR analysis showed that the S/MAR was tethered to the nuclear matrix in both fetal and adult hepatocytes. ChIP assay showed that, in adult hepatocytes, the S/MAR-GRE and the promoter proximal regions interacted with lamin and heterogeneous nuclear ribonucleoprotein U in a dexamethasone dependent manner, but this was not the case in fetal cells, suggesting that developmental stage-specific expression of the TO gene might rely on the binding of the enhancer (the -8.5kb S/MAR-GRE) and the promoter to the inner nuclear matrix.
Biochemical and Biophysical Research Communications 08/2009; 387(4):717-22. · 2.48 Impact Factor
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ABSTRACT: The glucocorticoid receptor regulates liver-specific expression of the tryptophan oxygenase gene through glucocorticoid responsive elements located -0.45 and -1.2 kb from the transcription start site. However, the hormone-mediated induction is restricted to adult hepatocytes, and fetal hepatocytes are unable to express the gene even in the presence of the receptor and glucocorticoid hormone. The difference in sensitivity to the hormone between adult and fetal hepatocytes has not been well understood. In this study, we analyzed the structure of the tryptophan oxygenase gene's promoter. The promoter has two TATA boxes, and transcription starts from the downstream TATA box. We found that a transcription factor GATA4 bound to the downstream TATA box and may inhibit the binding of TATA-binding protein, resulting in transcriptional repression even in the presence of glucocorticoid in fetal hepatocytes.
Cytotechnology 07/2008; 57(2):123-8. · 1.21 Impact Factor
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ABSTRACT: Chicken lysozyme is highly expressed in the oviduct. The 5' regulatory region of this gene contains a negative element that represses transcription. To assess the molecular basis underlying the regulation of lysozyme gene expression, we investigated the binding protein to this region. Sequence motif analysis suggested the existence of putative YY1 binding sites in this regulatory region. Electrophoretic mobility shift assay showed the specific binding of YY1 to the negative element. In addition, chromatin immunoprecipitation assay indicated that YY1 specifically bound to the negative element in oviduct cells but not in erythrocytes. It was suggested by electrophoretic mobility shift assay and chromatin immunoprecipitation assay that YY1 also bound to the negative regulatory region in the promoter of the ovalbumin gene which also shows oviduct-specific expression. Western blot analysis showed that YY1 was expressed in relatively high levels in the oviduct and nucleus fractionation experiments showed that YY1 was localized both in chromosome and nuclear matrix fractions. These results suggest that there are some specific roles in the negative regulatory regions of these genes in relation to the multifunctional transcription factor YY1.
Cytotechnology 12/2006; 52(3):159-70. · 1.21 Impact Factor
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ABSTRACT: The sumoylation of CCAAT/enhancer-binding proteins (C/EBPs) by small ubiquitin-related modifier-1 (SUMO-1) has been reported recently. In this study, we investigated the functional role of the sumoylation of C/EBPalpha in the differentiation of hepatocytes. The amount of sumoylated C/EBPalpha gradually decreased during the differentiation, which suggests that the sumoylation is important for the control of growth/differentiation especially in the fetal liver. To analyze the function of the sumoylation of C/EBPalpha in liver-specific gene expression, we studied its effects on the expression of the albumin gene. The C/EBPalpha-mediated transactivation of the albumin gene was reduced by sumoylation of C/EBPalpha in primary fetal hepatocytes. The enhancement of C/EBPalpha-mediated transactivation by BRG1, a core subunit of the SWI/SNF chromatin remodeling complex, was hampered by sumoylation in a luciferase reporter assay. In addition, we discovered that sumoylation of C/EBPalpha blocked its inhibitory effect on cell proliferation by leading to the disruption of a proliferation-inhibitory complex because of a failure of the sumoylated C/EBPalpha to interact with BRG1. BRG1 was recruited to the dihydrofolate reductase promoter in nonproliferating C33a cells but was not detected in proliferating cells where C/EBPalpha, BRG1, and SUMO-1 were overexpressed. This result suggests that BRG1 down-regulates the expression of the dihydrofolate reductase gene. These findings provide the insight that SUMO acts as a space regulator, which affects protein-protein interactions.
Journal of Biological Chemistry 09/2006; 281(31):21629-39. · 4.77 Impact Factor
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ABSTRACT: The chromatin remodeling complex SWI/SNF is known to regulate the transcription of several genes by controlling chromatin structure in an ATP-dependent manner. SWI/SNF contains the Swi2p/Snf2p like ATPases BRG1 or BRM exclusively. We found that the expression of BRM gradually increases and that of BRG1 decreases as liver cells differentiate. Chromatin immunoprecipitation assays revealed that the ATPase subunits of SWI/SNF and tumor suppressor retinoblastoma (RB) family proteins bind to the promoter region of the albumin gene in hepatocytes, and that the replacement of BRG1 with BRM and pRB with p130 at this site occurs over the course of differentiation. Small interfering RNA experiments showed that blocking the expression of BRG1 and BRM in fetal and adult hepatocytes, respectively, causes a reduction in albumin expression. In luciferase reporter assays with a pREP4-based reporter plasmid that forms a chromatin structure, BRG1 showed activity stimulating the expression of the albumin promoter mediated by CCAAT/enhancer-binding protein alpha (C/EBPalpha). This enhancement was facilitated by the RB family members pRB and p130. ATPase assays showed that both pRB and C/EBPalpha proteins directly stimulate the ATPase activity of BRG1. Our findings suggest that the mechanism by which the activity of transcription factors is enhanced by RB family members and SWI/SNF includes an increase in the ATPase activity of the chromatin remodeling complex.
Journal of Biochemistry 03/2006; 139(2):177-88. · 2.37 Impact Factor
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ABSTRACT: The chromatin remodeling complex, SWI/SNF, is known to regulate the transcription of several genes by altering the chromatin structure in an ATP-dependent manner. SWI/SNF exclusively contains BRG1 or BRM as an ATPase subunit. In the present study, we studied the role of SWI/SNF containing BRM or BRG1 in the expression of the liver-specific tryptophan oxygenase (TO) and tyrosine aminotransferase genes. Chromatin remodeling factors significantly repressed the expression of these genes induced by glucocorticoid receptor and dexamethasone. Since the repression was not reversed by trichostatin A treatment, it seemed to be independent of the well-known histone deacetylase pathway. Knock-down of BRG1 by small interfering RNA reversed the repression in primary fetal hepatocytes. These results support a model in which SWI/SNF containing BRG1 represses late stage-specific TO gene expression at an early stage of liver development.
Journal of Biochemistry 11/2005; 138(4):457-65. · 2.37 Impact Factor
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ABSTRACT: Transcriptional coactivators, CREB-binding protein (CBP) and p300, exhibit high homology in structure and similar functions. In the present study, we analyzed the function of CBP and p300 proteins as transcriptional coactivators in the expression of albumin in hepatocytes. The expression levels of CBP and p300 were high in fetal hepatocytes, but low in adult ones. Immunoprecipitation assays showed that both CBP and p300 interacted with hepatocyte nuclear factor-1alpha (HNF-1alpha) in primary hepatocytes. Furthermore, CBP and p300 were co-precipitated without HNF-1alpha. Chromatin immunoprecipitation (ChIP) assays revealed that both CBP and p300 are located in the albumin promoter region in hepatocytes. These results suggested that HNF-1alpha, CBP and p300 were incorporated into a preinitiation complex of RNA polymerase II at the albumin promoter. Luciferase reporter assays showed that CBP and p300 cooperatively triggered HNF-1alpha-mediated transcription of the albumin promoter. In addition, inhibition of CBP or p300 using small interfering RNAs (siRNAs) resulted in a reduction in albumin expression. These results suggest that both CBP and p300 are required for enhanced expression of albumin.
Journal of Biochemistry 10/2004; 136(3):313-9. · 2.37 Impact Factor
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ABSTRACT: Transcriptional coactivators, CREB-binding protein (CBP) and p300, exhibit high homology in structure and similar functions. In the present study, we analyzed the function of CBP and p300 proteins as transcriptional coactivators in the expression of albumin in hepatocytes. The expression levels of CBP and p300 were high in fetal hepatocytes, but low in adult ones. Immunoprecipitation assays showed that both CBP and p300 interacted with hepatocyte nuclear factor-1α (HNF-1α) in primary hepatocytes. Furthermore, CBP and p300 were co-precipitated without HNF-1α. Chromatin immunoprecipitation (ChIP) assays revealed that both CBP and p300 are located in the albumin promoter region in hepatocytes. These results suggested that HNF-1α, CBP and p300 were incorporated into a preinitiation complex of RNA polymerase II at the albumin promoter. Luciferase reporter assays showed that CBP and p300 cooperatively triggered HNF-1α–mediated transcription of the albumin promoter. In addition, inhibition of CBP or p300 using small interfering RNAs (siRNAs) resulted in a reduction in albumin expression. These results suggest that both CBP and p300 are required for enhanced expression of albumin.
